ThreePointFive Posted March 29, 2020 Share Posted March 29, 2020 (edited) I've been looking at this for some hours now and I'm not sure it's going to end without a fire, so I need some help. I know alternator wiring has been raised here many times, but this is slightly different. I have a P38 alternator with 3 contacts on the rear, standard stuff. Stole this photo to demonstrate: Left hand is the main output, D+ (middle) is the alternator to instruments connector and W (right) is for the rev counter. This is the TD5 wiring diagram. Three contacts, two the same as above, but no W due to the ECU-controlled rev counter, leaving one wire with nothing to connect to: So do I: dispense with the WG wire altogether put both onto the D+ terminal Put the WG wire on the W terminal forget about having a working charge warning light with this alternator Stop posting questions at 1am? I would just go and test this myself, but I don't have a completed instrument harness yet. I get that the lamp illuminates when there's a differential between the two, so surely they can't go on the same terminal? Really hoping I can keep this alternator for its 100amp goodness, but open to ideas. Edited March 29, 2020 by ThreePointFive Quote Link to comment Share on other sites More sharing options...
ianmayco68 Posted March 29, 2020 Share Posted March 29, 2020 I’m a bit lost , are you fitting this to a td5 engine ? Quote Link to comment Share on other sites More sharing options...
Escape Posted March 29, 2020 Share Posted March 29, 2020 A bit more info please. What car? I guess Disco2, as the Defender TD5 didn't have a rev counter as standard. If it's for an aftermarket rev counter in a Defender, just use a wire directly from the W-post to the gauge. That's what we did on my TD5 90, because the ECU rev signal would sometimes drop while winching. And what engine/ECU? GEMS/MS? There's a good chance you'll be able to use an output from the ECU to drive the gauge. Filip Quote Link to comment Share on other sites More sharing options...
steve200TDi Posted March 29, 2020 Share Posted March 29, 2020 It relates to this: So I guess 4.0 GEMS V8, with TD5 Defender vehicle loom and a P38 alternator. Quote Link to comment Share on other sites More sharing options...
ThreePointFive Posted March 29, 2020 Author Share Posted March 29, 2020 (edited) Sorry, should have said, but it is as Steve has posted. For this purpose, think of it as a TD5 Defender with a P38 alternator to keep it simple. Edited March 29, 2020 by ThreePointFive Quote Link to comment Share on other sites More sharing options...
western Posted March 29, 2020 Share Posted March 29, 2020 The dash warning light to the middle terminal, main cable to battery/starter to the left connection & rev counter to the right connection. the White/green trace could go on the same connection as the main cables, Quote Stop posting questions at 1am? that's good idea Quote Link to comment Share on other sites More sharing options...
ThreePointFive Posted March 29, 2020 Author Share Posted March 29, 2020 4 minutes ago, western said: The dash warning light to the middle terminal, main cable to battery/starter to the left connection & rev counter to the right connection. that's good idea Well Ralph, that last part certainly changes the tone that post can be read with. I hope your day gets better. The question I am asking - as badly worded as it may have been - from my understanding of the TD5 system is that essentially have two 'dash warning light' feeds, which go to different contacts on the TD5 alternator. I don't know if the W terminal can act as that 'extra' terminal, I suspect not given it has one job to do, but someone who understands more about the inner workings of these things might have be able to assist. Put rev counters to one side for the moment, that's not the issue in this case. Quote Link to comment Share on other sites More sharing options...
Bigj66 Posted March 29, 2020 Share Posted March 29, 2020 I’m not sure if this is of any help but I disconnected the alternator on my Thor 4.0 yesterday and noticed it only had two connections one heavy brown to the battery and a thin brown and yellow to terminal D+. If you can trace the WG wire that isn’t required and either strip it out or disconnect it then it should be safe. Quote Link to comment Share on other sites More sharing options...
western Posted March 29, 2020 Share Posted March 29, 2020 45 minutes ago, ThreePointFive said: Well Ralph, that last part certainly changes the tone that post can be read with. I hope your day gets better. The question I am asking - as badly worded as it may have been - from my understanding of the TD5 system is that essentially have two 'dash warning light' feeds, which go to different contacts on the TD5 alternator. I don't know if the W terminal can act as that 'extra' terminal, I suspect not given it has one job to do, but someone who understands more about the inner workings of these things might have be able to assist. Put rev counters to one side for the moment, that's not the issue in this case. Sorry it was meant to be light humoured, I was thinking that if the white/green goes to the B+ terminal, that would still give a feed to the 10amp fuse & the ignition switch, the Td5 alternator is a battery sense unit not a machine sense like the older vehicles & the alternator you have. Quote Link to comment Share on other sites More sharing options...
ThreePointFive Posted March 29, 2020 Author Share Posted March 29, 2020 (edited) 2 hours ago, western said: Sorry it was meant to be light humoured, I was thinking that if the white/green goes to the B+ terminal, that would still give a feed to the 10amp fuse & the ignition switch, the Td5 alternator is a battery sense unit not a machine sense like the older vehicles & the alternator you have. Well, you weren't wrong, I shouldn't be posting at that time of night! It's frustrating because it's a question that must have been addressed by others doing the same conversion as me, but I'm the only one that apparently can't work it out for myself. I think the best thing for me to do is just run it and if what lights up and goes out depending on connections to the B+. Edited March 29, 2020 by ThreePointFive Quote Link to comment Share on other sites More sharing options...
PaulMc Posted April 2, 2020 Share Posted April 2, 2020 Don't connect the WG wire to anything. It's an ignition switched live used by the TD5'S Denso alternator. It's not required on the P38 alternator. 1 Quote Link to comment Share on other sites More sharing options...
ThreePointFive Posted April 2, 2020 Author Share Posted April 2, 2020 (edited) Spot on Paul, thanks. I've re-purposed the other wire as the W terminal feed for the rev counter when I get one, so even that is useful now (running to a different connector). Must be the 5th time you've saved my build from myself. Edited April 2, 2020 by ThreePointFive Quote Link to comment Share on other sites More sharing options...
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